Currently, the TFT-LCD liquid crystal display on the mainstream market can be divided into three categories, namely, TN (Twisted Nematic) type, STN (Super Twisted Nematic) type, IPS (In-Plane Switching) type and VA (Vertical Alignment) type. The VA type LCD has high contrast relative to other types of LCD, the contrast can be reached 4000-8000, and has a very broad application in large-size display.
The VA type liquid crystal display has liquid crystal molecules arranged perpendicularly to the surface of the substrate without electric field in a dark state, which has no phase difference, low light leakage, low dark-state brightness, thereby having extremely high contrast.
For allowing the liquid crystal molecules in the VA type liquid crystal display panel to be arranged perpendicularly to the surface of the substrate, a vertical alignment needs to be applied to the liquid crystal molecules. As shown in FIG. 1, a liquid crystal display panel comprises a first substrate 10, a second substrate 20, a liquid crystal layer 30. The first substrate 10 has a first transparent electrode layer 11 disposed thereon, the second substrate 20 has a second transparent electrode layer 21 disposed thereon. A vertical alignment agent is coated on the inner sides of the first transparent electrode layer 11 and the second transparent electrode layer 21. The alignment agent generally includes great amount of chemical solvent NMP (N-Methyl pyrrolidone) and polymer such as polyimide (PI), then the two substrates is baked at high temperature (200° C., generally) for a long period, so that the alignment agent is dried to remove the solvent to respectively form a first PI alignment layer 12 on the inner side of the first substrate 10 and a second PI alignment layer 22 on the inner side of the second substrate.
During the process of manufacturing PI, it is necessary to uniformly apply the PI liquid on the surface of the substrate by an ink-jet printing technology, then the substrate is allowed to stand a period of time so that the PI liquid is diffused evenly on the surface of the substrate. Subsequently, the pre-baking step is carried out at a lower temperature (50-150 degrees) for a period of time (1 min to 10 mins), so that a part of the NMP (N-Methyl pyrrolidone) of the PI liquid is partially removed by evaporating to obtain a initially dried PI alignment layer. Then, a baking step is carried out at a high temperature (200-250 degrees) for a long time (30 mins to 120 mins), so that almost all of the solvent is evaporated, and carboxyl and amino groups of the polyamic acid in the PI liquid are fully cyclized to form polyimide. This shows that the manufacturing process of the PI alignment layer is more energy-consumed, not environmentally friend, and easy to cause harm to humans. In addition, due to the problems of uniformity, defect coating, and non-adhesive of the alignment layer, the product yield will be affected to result in a waste of resources, and thus the cost of production is increased.
It is therefore necessary to provide a liquid crystal medium composition to solve the problems existing in the conventional technology as described above.